As integrated circuit features continue to decrease in size and the number of components of an integrated circuit continues to increase, the requirements imposed upon the dielectrics commonly used in integrated circuit manufacture become more stringent. A dielectric is commonly deposited on the surface of a wafer and patterned to selectively expose portions of the surface. A metal or other conductive material, deposited on the surface of the dielectric, provides contacts to and between the individual devices. The surface of the dielectric must be reasonably planar so that the metal, typically aluminum, can be deposited without any electrical discontinuities. Such metal deposition becomes more difficult to perform as horizontal distances between devices decrease and the as deposited dielectric has a non-planar surface. Methods have been sought which planarize the dielectric surface. A typical method of planarizing a dielectric surface heats the dielectric and causes it to flow. However, the maximum temperature to which a circuit can be heated is lowered as, e.g., movement of dopants in the semiconductor must be restricted as junctions become shallower. The dielectric is typically SiO.sub.2 to which minor amounts of dopants, such as boron and phosphorus, are added to reduce the temperature at which the glass flows. Phosphorus also getters sodium and prevents its diffusion into junctions.
Several techniques, including chemical vapor deposition, have been used for dielectric deposition. One commonly used technique oxidizes, with oxygen, hydrides such as SiH.sub.4, B.sub.2 H.sub.6 (diborane) and PH.sub.3 (phosphine). This dielectric is typically referred to as BPSG (borophosphosilicate glass). Another technique decomposes an organo-silicon compound, such as tetraethylorthosilicate which is commonly referred to as TEOS. Other compounds, e.g., phosphine and trimethyl borate, are typically present as dopant sources. See, for example, Journal of Vacuum Science and Technology, B4, pp. 732-744, May/June 1986. This paper reports the low pressure deposition of borophosphosilicate glass using TEOS. The authors reported particle densities that were less than 0.2 per cm.sup.2. Later reports deal with the atmospheric pressure deposition of the dielectric. See, for example, NEC Research and Development, 94, pp. 1-7, July, 1989. The authors, who used ozone rather than oxygen, reported no measurable amounts of any unwanted impurities in the dielectric although surface particle concentrations were not reported.
We have found that TEOS films deposited at low pressure are preferable to those deposited at atmospheric pressure because they are smoother and have lower particulate counts. Also, TEOS films with both boron and phosphorus present in minor amounts, commonly referred to as BPTEOS, are preferred to BPSG films because they have better step coverage and a reduced tendency to flake off reactor surfaces. However, we have found that BPTEOS films have an unwanted tendency to accumulate particles during deposition.